以下代码是dispatch_get_current_queue 无法避免死锁的代码
- (void)test{ dispatch_queue_t queueA = dispatch_queue_create("queueA", NULL); dispatch_queue_t queueB = dispatch_queue_create("queueB", NULL); NSLog(@"A======%@， B=====%@",queueA, queueB); dispatch_sync(queueA, ^{ NSLog(@"A-------%@", dispatch_get_current_queue()); dispatch_sync(queueB, ^{ NSLog(@"B-------%@", dispatch_get_current_queue()); if(queueA != dispatch_get_current_queue()){ dispatch_sync(queueA, ^{ // queueA同步死锁 }); } }); }); }以下代码是dispatch_get_specific无法避免死锁的代码，与dispatch_get_current_queue是一模一样的，根本不像满世界的博客说的那样，用dispatch_queue_set_specific 和 dispatch_get_specific 来避免死锁。
const void * const dispatchSerialQueueSpecificKey = &dispatchSerialQueueSpecificKey; dispatch_queue_t queue = dispatch_queue_create("hahahahahahah", DISPATCH_QUEUE_SERIAL); dispatch_queue_set_specific(queue,dispatchSerialQueueSpecificKey, (__bridge void *)self, NULL); dispatch_async(dispatch_get_global_queue(0, 0), ^{ dispatch_sync(queue, ^{ id hh = (__bridge id)dispatch_get_specific(dispatchSerialQueueSpecificKey); const char * ha = dispatch_queue_get_label(dispatch_get_current_queue()); NSLog(@">>>>>>%p == %p , %s , %@ ",self,hh,ha, [NSThread currentThread]); dispatch_sync(dispatch_queue_create("ieueiwue", DISPATCH_QUEUE_SERIAL), ^{ id hh1 = (__bridge id)dispatch_get_specific(dispatchSerialQueueSpecificKey); const char * ha1 = dispatch_queue_get_label(dispatch_get_current_queue()); NSLog(@">>>>>>2 %p == %p , %s , %@ ",self,hh1,ha1,[NSThread currentThread]); if (hh1 != self) { dispatch_sync(queue, ^{ // queue同步死锁 NSLog(@">>>>>>>66666"); }); } }); }); });打印结果是
>>>>>>0x2832f1ac0 == 0x2832f1ac0 , hahahahahahah , <NSThread: 0x2832e9580>{number = 3, name = (null)} >>>>>>2 0x2832f1ac0 == 0x0 , ieueiwue , <NSThread: 0x2832e9580>{number = 3, name = (null)}从打印结果来看，hh1 用 dispatch_get_specific 取出来的是0x0，并没有取到 dispatch_queue_set_specific 塞进去的self。
造成了与dispatch_get_current_queue一样的后果，队列死锁。
